When photographing a moving object or at a slow shutter speed in hand-held photography, vibration is transmitted to the photographic system from shaking of the hand or hands holding the photographic system. This causes blurring of the photographed picture.
Various optical systems that are known as vibration-proof optical systems have been proposed for the purpose of preventing such blurring of a photographed picture, but many of these optical systems are for use in zoom lenses with a zoom ratio of six or greater with a narrow photographic area and are easily subject to blurring at the telephoto settings.
However, a small and lightweight digital camera with a zoom ratio of about three has recently become popular. Such a digital camera has improved portability due to its small size. However, its small size makes it difficult to hold the camera firmly enough to avoid blurring of photographed pictures due to movement of the camera during photographing.
Additionally, a zoom lens that includes, in order from the object side, a first lens group having negative refractive power and a second lens group having positive refractive power is preferred as the optical system of a digital camera with a zoom ratio of about three, but the smallest f-number at the telephoto end may be as large as about five in many of these zoom lenses, requiring longer exposures and thus increasing the probability of hand shaking causing blurring of the photographs.
In order to address this problem, a zoom lens having two components, positive and negative, has been proposed that moves the entire second lens group in a direction perpendicular to the optical axis of the zoom lens so that the optical axis of the entire second lens group becomes offset from and parallel to the optical axis of the zoom lens in order to correct for shaking of the zoom lens. This defines an eccentric position of the entire second lens group relative to the optical axis of the zoom lens. See, for example, Japanese Laid-Open Patent Application H6-337374 and Japanese Examined Patent Publication H07-060223.
Additionally, a zoom lens having two components, negative and positive, has been proposed that divides the second lens group into a first lens subgroup on the object side having positive refractive power and a second lens subgroup having positive refractive power and moving only the first lens subgroup in a direction perpendicular to the optical axis of the zoom lens so that the optical axis of the first lens subgroup becomes offset from and parallel to the optical axis of the zoom lens in order to correct for shaking of the zoom lens. See, for example, Japanese Laid-Open Patent Application H10-161024.
Furthermore, a zoom lens having two components, negative and positive, has been proposed that divides the second lens group into a first lens subgroup on the object side having positive refractive power and a second lens subgroup having positive refractive power and moving only the second lens subgroup in a direction perpendicular to the optical axis of the zoom lens so that the optical axis of the second lens subgroup becomes offset from and parallel to the optical axis of the zoom lens in order to correct for shaking of the zoom lens. See, for example, Japanese Laid-Open Patent Application H10-161023.
However, the zoom lenses of Japanese Laid-Open Patent Application H6-337374 have problems of a large load of the vibration-proof drive system because the entire second lens group is moved in correcting for shaking that occurs in hand-held operations.
The zoom lenses of Japanese Laid-Open Patent Application H10-161024 have an advantage of a small load of the vibration-proof drive system because only the first lens subgroup of the second lens group moves perpendicular to the optical axis of the zoom lens in order to correct for shaking vibration. However, in the case of an optical system for a digital camera, a shutter unit is frequently mounted on the object side of the second lens group. This creates a problem in the positioning of the vibration-proof drive system provided in the first lens subgroup of the second lens group interfering with the positioning of the shutter unit, thus making this arrangement undesirable.
Similarly, the zoom lenses of Japanese Laid-Open Patent Application H10-161023 have an advantage of a small load of the vibration-proof drive system because only the second lens subgroup of the second lens group moves perpendicular to the optical axis of the zoom lens in order to correct for shaking vibration. However, in the zoom lenses of Japanese Laid-Open Patent Application H10-161023, there has been a problem in that the refractive power of the second lens subgroup relative to the refractive power of the first lens subgroup becomes too large, resulting in deterioration of performance in recent digital cameras that have a large number of pixels and high resolution using solid state image pickup elements, such as a CCD, due to moving the second lens subgroup of the second lens group perpendicular to the optical axis of the zoom lens in order to prevent blurring, even if such performance deterioration is allowable for 35 mm photographic film cameras.